1. Field of the Invention
The present invention relates to a novel thermoplastic polymer composition. More specifically, it relates to a thermoplastic polymer composition containing (i) styrene polymer and (ii) an ionically crosslinked product of a modified block copolymer of an aromatic vinyl compound and a conjugated diene compound, which is modified with a dicarboxylic acid or derivative thereof. The term "styrene polymer" as used herein means both polystyrene and styrene-containing copolymer.
2. Description of the Prior Art
Polymer compositions of (i) styrene polymers, typically polystyrene and (ii) block copolymers of aromatic vinyl compounds and conjugated diene compounds, typically styrene-butadiene block copolymers containing up to 70% by weight, preferably up to 50% by weight, of styrene are known. These polymer compositions are useful as those in which the impact resistance of the styrene polymers is improved when the styrene polymers are present as a major constituent in the compositions. Contrary to this, in the case where the block copolymers of aromatic vinyl compounds and conjugated diene compounds, which are a so-called "thermoplastic elastomer", are present as a major constituent in the compositions, such compositions are known as those in which the hardness, tensile strength, oil resistance and other properties are improved as compared with the block copolymers. In addition to the above-mentioned characteristics, since the polymer compositions containing both styrene polymers and the aromatic vinyl compound-conjugated diene compound block copolymer can be readily molded or processed, these polymer compositions are widely utilized as various molding materials, in the fields of, for example, food containers, packaging materials, toys and ordinary utensils.
Furthermore, block copolymers of aromatic vinyl compounds and conjugated diene compounds having a conjugated diene content of about 30% by weight or less are resinous and are noted as those in which the impact resistance of the styrene polymers is improved, while the transparency of the styrene polymers, especially polystyrene is retained. The compositions of (i) the above-mentioned resinous block copolymers of aromatic vinyl compounds and conjugated diene compounds and (ii) styrene polymers such as general-purpose polystyrene or high-impact polystyrene are also known as compositions having transparency and impact resistance and suitable for use in the fields of various molded articles.
Previously, we found that polymer compositions of (i) styrene polymers and (ii) modified block copolymers of aromatic vinyl compounds and conjugated diene compounds which are modified with unsaturated carboxylic acids or the derivatives thereof had improved mechanical and chemical properties as compared with polymer compositions of the styrene polymers and the aromatic vinyl compound-conjugated diene compound block copolymers.
However, the above-mentioned polymer compositions still do not satisfactorily meet the recent demand in the fields of various molding materials.